This invention relates to an electric drive system for a vehicle.
Vehicle electric drive systems or AC electric traction drives have been proposed to overcome some of the deficiencies of mechanical transmission systems, such as a limited number of speeds, increased costs of engineering and manufacturing components, and limiting vehicle configuration options. One such hybrid electric drive system for a vehicle is described in U.S. Pat. No. 6,492,785, issued 10 Dec. 2002 and assigned to the assignee of this application. This hybrid electric drive system includes an engine driven electrical generator and electric motors for driving the traction wheels or belts, and for driving auxiliary power units such as the PTO or fan drives.
This hybrid electric drive system also includes a speed control pedal, and a forward-neutral-reverse directional control lever. With such controls, the operator can select one of several operating modes, including a mode wherein vehicle motion can be initiated by switching the directional control into the forward or reverse position and moving the speed control into a non-zero speed position. In this mode, the operator may quickly reverse direction by simply switching the directional control to the opposite direction. This is useful, for example, when operating a loader, where it is desirable to change direction quickly and often.
Both conventional tractors and tractors with infinitely variable transmissions (IVT) employ interlocks to prevent the operator from inadvertently starting the tractor in an unsafe condition. For example, many tractors sense transmission gear engagement and prevent the engine from starting if the transmission is engaged. Such an interlock cannot be used with a hybrid electric vehicle, because there is not a transmission with a gear ratio to be sensed.